This invention relates to passive vibration isolators of the type shown generally by U.S. Pat. No. 3,322,379, and deals more particularly with an improvement in such an isolator directed toward enhancing its utility by making it installable in a wide variety of different shapes of space which may exist between the two bodies with which it is used.
In addition to the general showing of U.S. Pat. No. 3,322,379, other forms of vibration isolators of the type with which this invention is concerned are shown by U.S. Pat. Nos. 3,441,238; 3,445,080; and 3,552,694. In each case illustrated by these patents the isolator serves to connect two bodies which vibrate relative to one another along a given line referred to herein as the line of action. The bodies are elastically restrained, by springs or the like, with regard to their movement along the line of action, and the isolator includes an inertia bar which moves in response to the relative motion between the two bodies. This motion of the inertia bar produces forces along the line of action which, at a certain "antiresonant" frequency, exactly balance, or almost exactly balance, the forces which the excited body would otherwise impose on the other body.
In some cases, where the relative motion of the two bodies occurs along a single line, a single isolator may be used to connect the two bodies. However, in other cases two or three isolators or sets of isolators may be used to accommodate components of vibration occurring along either two or three orthogonal axes.
One field of use of the isolators is in aircraft where, for example, a group of isolators may be used to isolate the rotor drive system of a helicopter from the remainder of the helicopter body. The helicopter rotor is usually driven at a fairly constant rpm and, therefore, the isolators may be tuned to have antiresonant frequencies equal to the rotor rpm or some multiple thereof. In all of the isolator constructions shown by the aforementioned patents the inertia bars are arranged with their longitudinal axes perpendicular to the line of action, but in aircraft installations the space available between the two vibrating bodies is often limited making it difficult in many cases to install such vibration isolators while keeping their inertia bars at the required perpendicular arrangement to the line of action.
This invention, therefore, provides an improved form of dynamic antiresonant vibration isolator wherein the orientation of the inertia bar longitudinal axis is independent of the orientation of the line of action, this accordingly allowing the isolator to be designed to fit many different space situations and to allow it to be installed in places where isolators of the previous designs could not be conveniently fitted.
Other objects and advantages of the invention will be apparent from the following detailed description of the preferred embodiments thereof.